My parts man says it will work fine but you have to change the spring in the bottom sheave to the 2388 model. Otherwise there is not enought tension on the belt because it is a stiffer and thicker belt.
I dont believe the 2100 or the 2300 series belts fit the 1600 series machines, as if i remember correctly, the 21 an 2300, have a 3speed rotor gearcase, And takes a longer belt, As the 1600series machines are just a 2 speed gear box, And yes the 1680 Heavy Duty Belt has the raised ribbs on top, As its all i use
2388 rotor belts will NOT fit a 2188 or older. The 2388 rotor belt is 3" longer to accomodate the 3-speed gearbox found only on the 2388 as well as the bigger sheaves on the 2388 rotor drive. 2188s through 1480s all take the same belt, 1440s through 2366s all take the same rotor belt. The last I knew CaseIH offered 2 different rotor belts for the 1480-2188 models and 1440-2366 models-a "standard" rotor belt and a heavy-duty rotor belt.